GB1520318A - Microphone assemblies - Google Patents

Abstract

1520318 Microphones; microphone circuits SONY CORP 13 Oct 1975 [31 Oct 1974] 41852/75 Heading H4J A microphone assembly (Fig. 2) comprises a housing 1 including a cylindrical capsule 2 and a smaller cylindrical projection 3, a microphone unit 5 being secured in a cavity 2a within the capsule 2. The capsule 2 acts as a windshield but has apertures 2p therethrough for transmission of sound into the cavity 2a. The projection 3 is adapted for insertion into the ear canal of a human head or a corresponding canal of a dummy head. The capsule 2 and projection 3 are preferably integrally moulded from plastics material. Alternatively part or all of the capsule 2 may be of metal or plastics mesh. The projection 3 preferably has a bore 4 so that when the microphone assembly is used on a human head the sound may be monitored by the wearer. The cable 6 from the microphone unit 5 is clipped to the user's hat (Fig. 3, not shown) or spectacles to avoid contact noise with the user's skin. Two such microphones are used, one on each side of the head, for stereophonic sound pick-up. The microphone unit 5 is preferably of electret type. Such an assembly has peaks in the frequency characteristic and these are smoothed out by tuned circuits. Fig. 5 shows a circuit in which the output of an electret microphone transducer q is applied to a F.E.T. 11 in a pre-amplifier 10 having a load resistor 13. The pre-amplifier 10 is connected through a two core shielded cable 6 to an amplifier 14 including a transistor 15. The amplifier 14 has tuned circuits 19 and 20 which eliminate peaks in the frequency response of the-assembly at 3 kHz and 8 kHz respectively. The circuits 19 and 20 may be tunable to suit individual requirements. The circuitry is also shown in Fig. 11 of co-pending Specification 1,520,319.